The Raton-Clayton Volcanic Field is a region of volcanic activity in northeastern New Mexico that has been active periodically, beginning at the western edge of the field with the Raton Phase from 9 to 3 million years ago. The Capulin Phase began about 1 million years ago at the center of the field. Capulin Volcano erupted approximately 60,000 years ago, when mammoths and giant bison roamed these plains. The flat topped mesas across the region are ancient lava flows, and the mountains are cinder cones, shield volcanos, tuff rings, and volcanic domes.